The present invention relates to a control device for an electronic digital display in an electronic instrument, particularly a timing unit. The device includes a first pulse generator to produce counting pulses, an electronic counting unit comprising one or more pulse counters, a display control device operated by at least one control element and comprising a second pulse generator which consists of a pulse transmitter having one or more pulse generating elements connected to it and an electrical counter. The pulse generating element or elements and the counter can be moved relative to each other to produce electric pulses of varying pulse frequency for the control of a display.
A control device of this type is disclosed in U.S. Pat. No. 4,091,612, which describes a set of pulse generators which produce pulses for resetting an electronic digital display. The input rate of these pulse generators is limited to approximately 200 pulses per second. Therefore, in order to reset the display of a timing unit by several hours, the pulse generator must go through a considerable number of turns until the desired display figure is reached, a process which is not conveneint for the person operating the unit.
The input rate of the disclosed pulse generator can not be increased without the use of special measures, due to mechanical difficulties concerning the contacts, particularly impact phenomina. Furthermore, the processing time problems of the electronics limit the rate of pulse generation.
This last mentioned difficulty will arise if a microprocessor is being used which must perform, in addition to the handling of the input pulses for the digital display, a number of operations controlling the electronic instrument. The microprocessor must carry out its various programmed tasks during a series of cycles by interrogating the relevant data during each program cycle, for example, the information originated by the second pulse generator. The microprocessor can therefore acquire the data of the second pulse generator only during a brief period of time within its program cycle, while the period of time before the next program cycle is relatively long. If the pulse generation by the second pulse generator is accomplished quickly, the pulses so generated will occur at a period of time during which the microprocessor is not interrogating the second pulse generator, and the corresponding pulses will then be lost.